Recently, semiconductor laser diodes have come to be widely used in a variety of types of electrical equipment, for example, laser printers, optical disk apparatuses, fiber-optic communication apparatuses, and mobile phones, because of their compact size, low cost, and ease of use.
However, the current/quantity of light characteristic of the semiconductor laser diode is dependent on temperature. Accordingly, it is necessary to control quantity of light to obtain a predetermined quantity of light reliably. This quantity of light control is called Automatic Power Control (APC). In the APC process, before the semiconductor laser diode is actually driven, the laser diode is driven in advance, the quantity of light from the laser diode is received by a photo diode (PD), and the detection current values of corresponding quantities of light are stored in a storage device. Then, the laser diode is controlled using the current values saved in the storage device so as to obtain a desired quantity of light reliably.
Recently, in connection with improvements in writing speed to write data in a storage device such as a semiconductor memory, a multi-beam laser method has come to be widely employed in the image forming apparatus. In the multi-beam laser method, multiple semiconductor lasers are provided to form a laser array, and each semiconductor laser is driven at the same time.
In such an image forming apparatus employing the multi-beam laser method, the photo diodes are installed to perform APC. Generally, in the image forming apparatus using the multi-beam laser method, a number of photo diodes is less than a number of the semiconductor laser diodes, further, only one diode may be employed in some case. By contrast, in the image forming apparatus employing a single beam laser method that will be described later, one photo diode is provided for one corresponding laser diode.
Using the multi-beam laser method described above, it is possible to achieve a high speed image forming apparatus and obtain a high quality image. Accordingly, there is more frequent adoption of the multi-beam laser method in the image forming apparatuses.
At the same time, there is increasing demand for a color image forming apparatus. For the color image forming apparatus, a lot of drive methods to drive lasers that form images by, for example, four color components, yellow (Y), magenta (M), cyan (C), and black (K) have been created.
When the multi-beam laser method is applied to laser diodes for four color components, a complicated and advanced control system is required, resulting in an expensive image forming apparatus. Accordingly, most general-purpose image forming apparatuses commercially used in the office currently employ multiple circuits for the single beam laser method using a laser diode-photo diode integrated (LD-PD) pair type system.
Accordingly, there is increasing demand for the semiconductor laser diode drive circuit which drives multiple laser diodes regardless of whether the single beam laser method is employed or the multi beam laser method is employed.
Currently, when the image forming apparatus employs the multi beam laser system, a special semiconductor laser drive circuit dedicated to the multi beam laser method is used. Further, when the image forming apparatus employs multiple single beam laser systems, multiple special semiconductor laser drive circuits dedicated to the single beam laser method are generally used.
JP-3542472-B and JP-2000-353851-A disclose example circuit configurations of the special semiconductor laser drive circuit dedicated to the multi beam laser method. However, in both circuit configurations, one photo diode is provided for multiple laser diodes corresponding to multiple channels (ch). Accordingly, they are not suitable for the system to drive the single beam laser system with the single beam laser method. When the circuit configurations described therein are applied to the single beam laser system, a special control is required compared to a case of driving a multi beam laser system.
Further, it may be possible to employ multiple semiconductor laser drive circuits dedicated to the single beam laser system to drive lasers of the multi beam laser system, however, a special control is required also. For this reason, it is necessary to develop a special semiconductor laser drive circuit dedicated to the multi beam laser system, or to the single beam laser system with each new system design, resulting in a cost penalty. Further, a relatively long term is required to develop the overall image forming apparatus.